Interestingly enough, according to Jim Milles' Mail Server Commands
file (GET MAILSER CMD, email [log in to unmask]) all of
the ones that he documents, save MAILBASE, do respond to the syntax:
 
UNSUBSCRIBE listname
 
Thus, you could compose one e-mail messages with multiple
recipients with multiple unsubscribes e.g.,
 
to: listserv@searn, listproc@somehost
 
unsubscribe lstown-l
unsubscribe lstsrv-l
unsubscribe proclist-l
 
Of course SEARN would only respond positively for the first
two unsubs, whereas SOMEHOST would only respond to the last.
 
Of course LISTSERV syntax allows an asterisk for the listname
which is a wildcard.  If you are going to mix n' match MLMs
though, I would not use the asterisk since it might prematurely
terminate the command stream.
 
From Jim's document:
 
Leave a list:
     Listproc:      UNSUBSCRIBE [listname]
     LISTSERV:      SIGNOFF [listname]
                    -- or --
                    UNSUBSCRIBE [listname]
     Mailbase:      LEAVE [listname]
     Mailserv:      UNSUBSCRIBE [listname]
                    (UNSUBSCRIBE [listname] [address]
                    if you subscribed under a different e-mail
                    address.)
     Majordomo:     UNSUBSCRIBE [listname]
                    (UNSUBSCRIBE [listname] [address]
                    if you subscribed under a different e-mail
                    address.)
 
--  co-owner INFOSYS, TQM-L, CPARK-L, ERAPPA-L, JANITORS, LDBASE-L, et -L
URL:mailto:[log in to unmask]          "Kids: don't e-mail to strangers!"